Philadelphia Eagles' Alshon Jeffery (17) catches a pass in front of Carolina Panthers' Kevon Seymour (27) in the second half of an NFL football game in Charlotte, N.C., Thursday, Oct. 12, 2017. (AP Photo/Mike McCarn)

Philadelphia Eagles' Carson Wentz (11) is upended by Carolina Panthers' James Bradberry (24) in the second half of an NFL football game in Charlotte, N.C., Thursday, Oct. 12, 2017. (AP Photo/Mike McCarn)

Carolina Panthers' Luke Kuechly (59) and Kawann Short (99) wear a #51 decal on their helmets as they warm up before an NFL football game against the Philadelphia Eagles in Charlotte, N.C., Thursday, Oct. 12, 2017. The 51 is in honor of former Carolina Panthers linebacker and coach Sam Mills, who died of cancer. (AP Photo/Mike McCarn)

CHARLOTTE, N.C. (AP) — Carolina Panthers star linebacker Luke Kuechly is back in the concussion protocol. And that could leave a big hole at the heart of the Panthers' defense.

Kuechly left the Panthers' 28-23 loss to the Philadelphia Eagles in the first half Thursday night after taking a hit near the left side of his neck. He walked to the sideline and later jogged to the tunnel but didn't return to the field with his teammates at the start of the third quarter before being ruled out for the game.

Now the Panthers will have to wait to find out Kuechly's status for Week 7 trip to Chicago.

"All I can tell you is he's in the protocol," Panthers coach Ron Rivera said, adding: "I don't know anything other than that."

It marks the third straight year the former Associated Press NFL defensive player of the year has dealt with concussion issues, which have cost him nine games over the past two seasons. And it followed the scary visual from last season when Kuechly was carted off the field while sobbing uncontrollably.

This play seemed far more routine, with Kuechly going low as he took a hit from offensive lineman Brandon Brooks on a run by LeGarrette Blount.

Brooks' left arm and shoulder collided with Kuechly near his left shoulder and helmet as he went to the ground. Moments later, Kuechly paused to squat down on the field with 5:19 left in the second quarter, then walked to the sideline for trainers to test the range of motion in his neck before he jogged into the locker-room tunnel.

"Last year was a little scarier," Panthers cornerback James Bradberry said. "This year I had just seen Luke walking away. It looked like he had full consciousness. I figured it was his shoulder or something. I wasn't sure."

Instead, Kuechly didn't join the team for the second half and was ruled out in the third quarter.

"I'm sure that the air kind of went out of the building," Bradberry said.

And Philadelphia took advantage, scoring all three of its touchdowns after Kuechly's exit — the first coming five plays after his injury. As Eagles coach Doug Pederson put it: "It can change for us on offense without him in there."

Now the Panthers face the uncertainty of how long Kuechly could be out. He missed three games with a concussion in 2015, then went on to miss six games after last year's concussion. In that case, Kuechly was in the protocol for three games then was cleared to return, but Rivera held him out as the Panthers closed a playoff-less season.

"We care about Luke as a person," Panthers cornerback Captain Munnerlyn said. "I love Luke the player and I love Luke as a person. We definitely are concerned about that. We're definitely concerned about his health. Hopefully it's not that bad. Hopefully he can be back with us. We don't know, so we'll see."